Numerous UV-protective glass (oxides) and plastic lens compositions have been previously described. Often, a trade-off exists between strength or mechanical properties and UV absorbance. For example, plastic lenses are lightweight due to their low densities; they can also be formed thinner than most glasses to further reduce weight. They also generally absorb UV radiation better than their glass counterparts. However, glass lenses, while typically heavier and thicker, are more scratch resistant and have better mechanical strength. Both glass and plastic lenses may be tinted a variety of colors, with the most common being green, gray, and brown.
One strategy for improving UV absorbance of glass lenses involves adding a cuprous or cuprous-cadmium halide crystal phase to non-photochromic colorless borosilicate glass. UV absorbance is improved in these glasses; however, the relative proportions of the oxide components in such compositions must be adjusted to maintain basicity. Thus, the use of alkali metals and alkaline earth metals is limited, which can adversely affect mechanical and optical properties.
An alternative strategy for improving UV absorbance of glass lenses involves the addition of silver salts to the glass composition, including a final hydrogen firing step to product a tint. However, the thickness of such glasses must be kept above about 1.8 mm when fabricated as lenses to insure adequate mechanical strength.
Thinner glass lenses with good mechanical properties have also been prepared, but are not designed to absorb UV radiation. Instead, they are designed to be used as laminates, with at least some of the scratch resistance and mechanical strength imparted by the additional laminated layers.
Consequently, there is a need for a thin glass material with the UV absorption capabilities of plastic and the high mechanical strength of glass. Ideally, small amounts of coloring agents could be used to produce a tint in these glasses without affecting optical or mechanical properties. The present application addresses this need.